Browsing by Subject "Mutual information"
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Item Open Access Computer Aided Detection of Masses in Breast Tomosynthesis Imaging Using Information Theory Principles(2008-09-18) Singh, SwateeBreast cancer screening is currently performed by mammography, which is limited by overlying anatomy and dense breast tissue. Computer aided detection (CADe) systems can serve as a double reader to improve radiologist performance. Tomosynthesis is a limited-angle cone-beam x-ray imaging modality that is currently being investigated to overcome mammography's limitations. CADe systems will play a crucial role to enhance workflow and performance for breast tomosynthesis.
The purpose of this work was to develop unique CADe algorithms for breast tomosynthesis reconstructed volumes. Unlike traditional CADe algorithms which rely on segmentation followed by feature extraction, selection and merging, this dissertation instead adopts information theory principles which are more robust. Information theory relies entirely on the statistical properties of an image and makes no assumptions about underlying distributions and is thus advantageous for smaller datasets such those currently used for all tomosynthesis CADe studies.
The proposed algorithm has two 2 stages (1) initial candidate generation of suspicious locations (2) false positive reduction. Images were accrued from 250 human subjects. In the first stage, initial suspicious locations were first isolated in the 25 projection images per subject acquired by the tomosynthesis system. Only these suspicious locations were reconstructed to yield 3D Volumes of Interest (VOI). For the second stage of the algorithm false positive reduction was then done in three ways: (1) using only the central slice of the VOI containing the largest cross-section of the mass, (2) using the entire volume, and (3) making decisions on a per slice basis and then combining those decisions using either a linear discriminant or decision fusion. A 92% sensitivity was achieved by all three approaches with 4.4 FPs / volume for approach 1, 3.9 for the second approach and 2.5 for the slice-by-slice based algorithm using decision fusion.
We have therefore developed a novel CADe algorithm for breast tomosynthesis. The techniques uses an information theory approach to achieve very high sensitivity for cancer detection while effectively minimizing false positives.
Item Open Access Knowledge-Based IMRT Treatment Planning for Bilateral Head and Neck Cancer(2013) Schmidt, Matthew CharlesIntensity-modulated radiotherapy (IMRT) remains the standard of care for external beam radiation therapy for head and neck cancers. Planning for IMRT requires a trial-and-error approach that is completely dependent on planner expertise and time available for multiple iterations of manual optimization adjustments. Knowledge-based radiation therapy planning utilizes a database of previously planned Duke University Medical Center patient plans to create clinically comparable treatment plans by comparing the geometrical two-dimensional projections of the planning target volume (PTV) and organs at risk (OAR). These 2D beam's eye view (BEV) images are first aligned with squared error registration, then the similarity is computed using the mutual information (MI) metric. After the closest match is found, computed constraints and deformed fluence maps are entered into Eclipse treatment planning system to generate the new knowledge-based treatment plan. For this study, 20 randomly selected cases were matched against a database of 103 head and neck cancer cases. The resulting new plans were compared to their clinically planned counterparts. For these 20 cases, 13 proved to be dosimetrically comparable by evaluation of the PTV dose-volume histogram. In 92% of cases planned, at least half of the OARs were also deemed comparable or better than the original plan. These cases were planned in less than 25 minutes with no manual constraint objective adjustments, as opposed to many hours needed in clinical planning.
Item Open Access Knowledge-Based IMRT Treatment Planning for Prostate Cancer: Experience with 101 cases from Duke Clinic(2012) Dick, DeonIntensity-modulated radiotherapy (IMRT) has become an effective tool for cancer treatment with radiation. However, even expert radiation planners still need to spend a substantial amount of time, approximately 4 hours, manually adjusting IMRT optimization parameters such as dose limits and costlet weights in order to obtain a clinically acceptable plan. Also, the quality of the treatment plan generated is solely based on the experience and training of the planning. In comparing the geometries of the planning target volume (PTV), bladder, rectum, right and left femoral heads, a knowledge-based approach to IMRT treatment planning may reduce the time needed to generate a clinically acceptable prostate plan. The knowledge-based approach uses the clinically acceptable plans of previously irradiated patients which are adapted to the new patient. Patient selection is done by using mutual information (MI). Having selected the best matched patient, Elastix (a toolkit for rigid and deformable registration) is used to deform the treatment plan of the previously irradiated patient to the new patient's geometry. The Eclipse treatment planning system is used to generate both pre-optimized and post optimized plans for the new patients. The knowledge-based treatment plans require no manual intervention. For the 101 patient data, it was shown that the newly generated plans were of similar or slightly worse dosimetric quality and were only generated in less than 30 minutes. Given the large size of this data set, the results are likely to be robust in representing treatment planning efficacy over a diverse range of patient anatomy. The results also show that this work has the potential to automatically provide high quality treatment plans while dramatically reducing the dependence of the expertise of the planner and the treatment planning time.
Item Open Access Tailored Scalable Dimensionality Reduction(2018) van den Boom, WillemAlthough there is a rich literature on scalable methods for dimensionality reduction, the focus has been on widely applicable approaches which, in certain applications, are far from optimal or not even applicable. Dimensionality reduction can improve scalability of Bayesian computation, but optimal performance needs tailoring to the model. What kind of dimensionality reduction is sensible in data applications varies by the context of the data, resulting in neglect of information contained in data that do not fit general approaches.
This dissertation introduces dimensionality reduction methods tailored to specific computational or data applications. Firstly, we scale up posterior computation in Bayesian linear regression using a dimensionality reduction approach enabled by the linearity in the model. It approximately integrates out nuisance parameters from a high-dimensional likelihood. The resulting posterior approximation scheme is competitive with state-of-the-art scalable posterior inference methods while being easier to interpret, understand, and analyze due to the explicit use of dimensionality reduction. Bayesian variable selection is considered as an example of a challenging posterior where the dimensionality reduction speeds up computation greatly and accurately.
Secondly, we show how to reduce dimensionality based on data context in varying-domain functional data, where existing methods do not apply. The data of interest are intraoperative blood pressure and heart rate measurements. The first proposed approach extracts multiple different low-dimensional features from the high-dimensional blood pressure data, which are partly predefined and partly learnt from the data. This yields insights regarding blood pressure variability new to the clinical literature since such detailed inference was not possible with existing methods. The concluding case of dimensionality reduction is quantifying coupling of blood pressure and heart rate. This reduces two time series to one measurement of the strength of coupling. The results show the utility for inference methods of dimensionality reduction that is tailored to the challenge at hand.